Product

Asterisk

Summary

Remote Crash Vulnerability in chan_sip channel driver

Nature of Advisory

Denial of Service

Susceptibility

Remote Unauthenticated Sessions

Severity

Minor

Exploits Known

No

Reported On

June 28, 2019

Reported By

Francesco Castellano

Posted On

July 1, 2019

Last Updated On

July 2, 2019

Advisory Contact

Jcolp AT sangoma DOT com

CVE Name

CVE-2019-13161

Description

When T.38 faxing is done in Asterisk a T.38 reinvite may be sent to an endpoint to switch it to T.38. If the endpoint responds with an improperly formatted SDP answer including both a T.38 UDPTL stream and an audio or video stream containing only codecs not allowed on the SIP peer or user a crash will occur. The code incorrectly assumes that there will be at least one common codec when T.38 is also in the SDP answer.

This requires Asterisk to initiate a T.38 reinvite which is only done when executing the ReceiveFax dialplan application or performing T.38 passthrough where a remote endpoint has requested T.38.

For versions of Asterisk 13 before 13.21.0 and Asterisk 15 before 15.4.0 the “preferred_codec_only” option must also be set to “yes”. If set to “no” the crash will not occur.

Resolution

If T.38 faxing is not required this functionality can be disabled by ensuring the “t38pt_udptl” is set to “no” so a T.38 reinvite is not possible.

If T.38 faxing is required then Asterisk should be upgraded to a fixed version. The problem can also be limited in scope by enabling T.38 faxing only for endpoints which actually participate in fax.

Affected Versions

Product

Release Series

Asterisk Open Source

13.x

All releases

Asterisk Open Source

15.x

All releases

Asterisk Open Source

16.x

All releases

Certified Asterisk

13.21

All releases

Corrected In

Product

Release

Asterisk Open Source

13.27.1

Asterisk Open Source

15.7.3

Asterisk Open Source

16.4.1

Certified Asterisk

13.21-cert4

Patches

SVN URL

Revision

http://downloads.asterisk.org/pub/security/AST-2019-003-13.diff

Asterisk 13

http://downloads.asterisk.org/pub/security/AST-2019-003-15.diff

Asterisk 15

http://downloads.asterisk.org/pub/security/AST-2019-003-16.diff

Asterisk 16

http://downloads.asterisk.org/pub/security/AST-2019-003-13.21.diff

Certified Asterisk 13.21

Links

https://issues.asterisk.org/jira/browse/ASTERISK-28465

Asterisk Project Security Advisories are posted at http://www.asterisk.org/security

This document may be superseded by later versions; if so, the latest version will be posted at http://downloads.digium.com/pub/security/AST-2019-003.pdf and http://downloads.digium.com/pub/security/AST-2019-003.html

Revision History

Date

Editor

Revisions Made

July 1, 2019

Joshua Colp

Initial revision